Oil wells typically vary in depth from a few hundred, feet to several thousand feet. In many wells there is insufficient subterranean pressure to force the oil to the earth's surface. For this reason some system must be devised for pumping the crude oil from the producing formation to the earth's surface. The most common system for pumping an oil well is by the installation of a pumping unit at the earth's surface that vertically reciprocates a string of sucker rods extending within tubing to a subsurface pump.
Traditionally sucker rod strings have been reciprocated by a device known as a pump jack which operates by the rotation of an eccentric crank driven by a prime mover which may be an engine or an electric motor. Such mechanical drive mechanism has been utilized extensively in oil production industry for decades and continues to be a primary method for extracting oil from a well. However, such mechanical systems suffer from a number of inherent disadvantages or inefficiencies that include their substantial size and weight that makes them expensive to produce, difficult to transport and expensive to install. The mass of such units also requires significant structural support elements at the wellhead which adds to the complexity and expense of the overall drive mechanism. Furthermore, mechanical drive systems have components that are physically linked or connected in some form by way of connecting rods, cams and gear boxes. For a variety of different reasons it often becomes necessary to adjust the travel of the pump rod. Mechanical linkages, as have been previously used, present difficulties in adjusting the travel or displacement of the pumping rods. With most mechanical pumping systems in present use adjusting the rod displacement or pumping speed requires the drive system to be shut down, wasting valuable production time and increasing labor costs. Mechanical drive pump jacks are also limited in their ability to control acceleration and deceleration of the pump rod during its reciprocation.
To combat these limitations in mechanical pump jack drive systems, others have provided a variety of different pneumatic and hydraulic drive mechanisms that have met varying degrees of success. Most hydraulic drive systems in use today are mounted above a stuffing box through which a polished rod extends. Below the stuffing box is a T-fitting so that produced oil is diverted from upward flow within the well tubing to a gathering line that connects to the stuffing box. Stuffing boxes require frequent lubrication. If not constantly lubricated, the packing in stuffing boxes soon wear out resulting in leakage that can spread crude oil to the environment. The invention herein provides an improved hydraulic operated pumping unit that, among other advantages, eliminates the need for a stuffing box.
Another aspect of the present invention is an improved reciprocated pump positioned at the lower end of a string of tubing supported in a borehole, the tubing providing a passageway for moving formation fluid to the earth's surface.
The pump system is formed of a pump barrel positioned in the borehole having an upper and a lower end. The upper end of the pump barrel is in communication with the tubing. A standing valve is positioned adjacent the lower end of the pump barrel and provides a first passageway through which formation fluid flows into the pump barrel.
The pump barrel has an intermediate vent port between the upper and lower ends, the vent port providing a second passageway by which formation fluid enters the barrel.
A tubular plunger is reciprocated within the barrel. The plunger has an upper and a lower end. A traveling valve controls fluid flow through the tubular plunger.
A plurality of individual non-metallic seal rings separated by metallic spacers are positioned on an upper portion of the plunger. The non-metallic seal rings engage the interior cylindrical surface of the pump barrel. The seal rings and metallic spacers are configured to support in substantially leak proof manner the column of formation fluid within the tubing extending to the earth's surface. The non-metallic seal rings and metallic spacers, in sealed relationship with the interior surface of the pump barrel provide a system, that substantially isolates the portion of the barrel below the non-metallic seal rings from the tubing pressure there above to thereby allow formation fluid to more freely flow into the pump barrel. That is, by fully supporting the weight of the produced fluid contained within the tubing extending from the pump barrel to the earth's surface, the area below the packing is thereby substantially at the formation fluid pressure so that no fluid pressure exists within the pump barrel to reduce the rate of fluid flow from the formation into the pump barrel. In this way the pump barrel more rapidly fills on each stroke of the plunger to more efficiently and effectively move formation fluid to the earth's surface as the plunger is reciprocated.